asbestos--crocidolite and Inflammation

Rare biallelic

Topics: Adult; Aged; Animals; Asbestos, Crocidolite; Asbestosis; Family; Female; Genetic Predisposition to Disease; Genomic Instability; Germ-Line Mutation; Heterozygote; Humans; Incidence; Inflammation; Male; Mesothelioma; Mice; Middle Aged; RecQ Helicases

Humans exposed to asbestos and/or asbestiform fibers are at high risk of developing many lung diseases including asbestosis, lung cancer, and malignant mesothelioma. However, the disease-causing potential and specific metabolic mechanisms and pathways associated with various asbestos/asbestiform fiber exposures triggering different carcinogenic and non-carcinogenic outcomes are still largely unknown. The aim of this this study was to investigate gene expression profiles and inflammatory responses to different asbestos/asbestiform fibers at the acute/sub-acute phase that may be related to delayed pathological outcomes observed at later time points. Mice were exposed to asbestos (crocidolite, tremolite asbestos), asbestiform fibers (erionite), and a low pathogenicity mineral fiber (wollastonite) using oropharyngeal aspiration. Similarities in inflammatory and tissue damage responses, albeit with quantitative differences, were observed at day 1 and 7 post treatment. Exposure to different fibers induced significant changes in regulation and release of a number of inflammatory cytokines/chemokines. Comparative analysis of changes in gene regulation in the lung on day 7 post exposure were interpretable in the context of differential biological responses that were consistent with histopathological findings at days 7 and 56 post treatment. Our results noted differences in the magnitudes of pulmonary responses and gene regulation consistent with pathological alterations induced by exposures to four asbestos/asbestiform fibers examined. Further comparative mechanistic studies linking early responses with the long-term endpoints may be instrumental to understanding triggering mechanisms underlying pulmonary carcinogenesis, that is lung cancer versus mesothelioma.

Topics: Animals; Asbestos, Amphibole; Asbestos, Crocidolite; Calcium Compounds; Female; Inflammation; Lung; Mice; Mice, Inbred C57BL; Silicates; Transcriptome; Zeolites

Upon inhalation, multi-walled carbon nanotubes (MWCNTs) may reach the subpleura and pleural spaces, and induce pleural inflammation and/or mesothelioma in humans. However, the mechanisms of MWCNT-induced pathology after direct intrapleural injections are still only partly elucidated. In particular, a role of the proinflammatory interleukin-1 (IL-1) cytokines in pleural inflammation has so far not been published. We examined the MWCNT-induced pleural inflammation, gene expression abnormalities, and the modifying role of IL-1α and β cytokines following intrapleural injection of two types of MWCNTs (CNT-1 and CNT-2) compared with crocidolite asbestos in IL-1 wild-type (WT) and IL-1α/β KO (IL1-KO) mice. Histopathological examination of the pleura 28 days post-exposure revealed mesothelial cell hyperplasia, leukocyte infiltration, and fibrosis occurring in the CNT-1 (Mitsui-7)-exposed group. The pleura of these mice also showed the greatest changes in mRNA and miRNA expression levels, closely followed by CNT-2. In addition, the CNT-1-exposed group also presented the greatest infiltrations of leukocytes and proliferation of fibrous tissue. WT mice were more prone to development of sustained inflammation and fibrosis than IL1-KO mice. Prominent differences in genetic and epigenetic changes were also observed between the two genotypes. In conclusion, the fibrotic response to MWCNTs in the pleura depends on the particles' physico-chemical properties and on the presence or absence of the IL-1 genes. Furthermore, we found that CNT-1 was the most potent inducer of inflammatory responses, followed by CNT-2 and crocidolite asbestos.

Topics: Animals; Asbestos, Crocidolite; Fibrosis; Inflammation; Interleukin-1; Mice; Mice, Inbred C57BL; Nanotubes, Carbon; Pleural Cavity

Translocation of multiwalled carbon nanotubes (MWCNTs) from the lung to the pleural cavity, deposition of the fibers in the pleural tissue, induction of pleural fibrosis, and mesothelial proliferation have been found in rodents administered MWCNTs by different pulmonary exposure methods. However, whether the translocation and deposition and the subsequent pleural inflammation are associated with the pleural lesions is unclear. In the present study, male F344 rats were given 250 μg of two types of MWCNTs, with crocidolite as a positive control, 2 times/week for 4 weeks by intratracheal spraying. At 24 h and at 3 months after the last spraying, the rats were sacrificed for histological examination of the lung and chest wall; pleural cavity lavage was also collected at sacrifice for observation of pleural inflammatory reactions. The results indicated that intratracheally sprayed MWCNTs, like crocidolite fibers, translocated into the pleural cavity, deposited in the pleura, and induced persistent infiltration of immune cells into the pleural cavity, persistent pleural fibrosis, and mesothelial proliferation. The number of MWCNT fibers detected in the pleural cavity lavage was parallel to the number of infiltrating immune cells, which were mainly composed of macrophages. Analysis of cytokines in the fluids of the pleural cavity lavages by suspension array indicated that levels of IL-2, IL-18, and IP-10 were significantly increased both at 24 h and at 3 months after the last spraying. In vitro proliferation assays revealed that a mixture of IL-2, IL-18, and IP-10, but not any of these cytokines alone, promoted cell proliferation of human fibroblasts and mesothelial cells. These results suggest that translocated and deposited MWCNTs induce subsequent pleural inflammation and that increased IL-2, IL-18, and IP-10 synergistically promote the development of pleural fibrosis and mesothelial proliferation.

Topics: Animals; Asbestos, Crocidolite; Bronchoalveolar Lavage Fluid; Cell Line; Cell Proliferation; Cytokines; Epithelial Cells; Fibrosis; Humans; Inflammation; Male; Nanotubes, Carbon; Pleura; Rats; Rats, Inbred F344

Malignant mesothelioma (MM), linked to asbestos exposure, is a highly lethal form of thoracic cancer with a long latency period, high mortality and poor treatment options. Chronic inflammation and oxidative tissue damage caused by asbestos fibers are linked to MM development. Flaxseed lignans, enriched in secoisolariciresinol diglucoside (SDG), have antioxidant, anti-inflammatory and cancer chemopreventive properties. As a prelude to chronic chemoprevention studies for MM development, we tested the ability of flaxseed lignan component (FLC) to prevent acute asbestos-induced inflammation in MM-prone Nf2(+/mu) mice. Mice (n = 16-17 per group) were placed on control (CTL) or FLC-supplemented diets initiated 7 days prior to a single intraperitoneal bolus of 400 µg of crocidolite asbestos. Three days post asbestos exposure, mice were evaluated for abdominal inflammation, proinflammatory/profibrogenic cytokine release, WBC gene expression changes and oxidative and nitrosative stress in peritoneal lavage fluid (PLF). Asbestos-exposed mice fed CTL diet developed acute inflammation, with significant (P < 0.0001) elevations in WBCs and proinflammatory/profibrogenic cytokines (IL-1ß, IL-6, TNFα, HMGB1 and active TGFß1) relative to baseline (BL) levels. Alternatively, asbestos-exposed FLC-fed mice had a significant (P < 0.0001) decrease in PLF WBCs and proinflammatory/profibrogenic cytokine levels relative to CTL-fed mice. Importantly, PLF WBC gene expression of cytokines (IL-1ß, IL-6, TNFα, HMGB1 and TGFß1) and cytokine receptors (TNFαR1 and TGFßR1) were also downregulated by FLC. FLC also significantly (P < 0.0001) blunted asbestos-induced nitrosative and oxidative stress. FLC reduces acute asbestos-induced peritoneal inflammation, nitrosative and oxidative stress and may thus prove to be a promising agent in the chemoprevention of MM.

Topics: Animals; Antioxidants; Asbestos, Crocidolite; Butylene Glycols; Chromatography, Liquid; Diet; Dietary Supplements; Disease Models, Animal; Enzyme-Linked Immunosorbent Assay; Flax; Glucosides; Inflammation; Lignans; Mesothelioma; Mice; Mice, Mutant Strains; Oxidative Stress; Peritoneal Lavage; Peritoneum; Precancerous Conditions; Reverse Transcriptase Polymerase Chain Reaction; Seeds; Tandem Mass Spectrometry; Transcriptome

Pulmonary exposure to multiwalled carbon nanotubes (MWCNT) induces an inflammatory and rapid fibrotic response, although the long-term signaling mechanisms are unknown. The aim of this study was to examine the effects of 1, 10, 40, or 80 μg MWCNT administered by pharyngeal aspiration on bronchoalveolar lavage (BAL) fluid for polymorphonuclear cell (PMN) infiltration, lactate dehydrogenase (LDH) activity, and lung histopathology for inflammatory and fibrotic responses in mouse lungs 1 mo, 6 mo, and 1 yr postexposure. Further, a 120-μg crocidolite asbestos group was incorporated as a positive control for comparative purposes. Results showed that MWCNT increased BAL fluid LDH activity and PMN infiltration in a dose-dependent manner at all three postexposure times. Asbestos exposure elevated LDH activity at all 3 postexposure times and PMN infiltration at 1 mo and 6 mo postexposure. Pathological changes in the lung, the presence of MWCNT or asbestos, and fibrosis were noted at 40 and 80 μg MWCNT and in asbestos-exposed mice at 1 yr postexposure. To determine potential signaling pathways involved with MWCNT-associated pathological changes in comparison to asbestos, up- and down-regulated gene expression was determined in lung tissue at 1 yr postexposure. Exposure to MWCNT tended to favor those pathways involved in immune responses, specifically T-cell responses, whereas exposure to asbestos tended to favor pathways involved in oxygen species production, electron transport, and cancer. Data indicate that MWCNT are biopersistent in the lung and induce inflammatory and fibrotic pathological alterations similar to those of crocidolite asbestos, but may reach these endpoints by different mechanisms.

Topics: Air Pollutants; Animals; Asbestos, Crocidolite; Bronchoalveolar Lavage Fluid; Dose-Response Relationship, Drug; Gene Expression; Inflammation; Inhalation Exposure; L-Lactate Dehydrogenase; Lung; Male; Mice; Mice, Inbred C57BL; Nanotubes, Carbon; Neutrophil Infiltration; Neutrophils; Pulmonary Fibrosis; Time Factors

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

Topics: Asbestos, Crocidolite; Carcinogenesis; Cell Line; Cell Proliferation; Cell Survival; Cluster Analysis; Dose-Response Relationship, Drug; Epithelial Cells; Gene Expression Profiling; Humans; Inflammation; Lung; Microarray Analysis; Signal Transduction; Silicon Dioxide

Malignant mesothelioma (MM) is an aggressive cancer of mesothelial cells of pleural and peritoneal cavities. In 85% of cases both pleural and peritoneal MM is caused by asbestos exposure. Although both are asbestos-induced cancers, the incidence of pleural MM is significantly higher (85%) than peritoneal MM (15%). It has been proposed that carcinogenesis is a result of asbestos-induced inflammation but it is not clear what contributes to the differences observed between incidences of these two cancers. We hypothesize that the observed differences in incidences of pleural and peritoneal MM are the result of differences in the direct response of these cell types to asbestos rather than to differences mediated by the in vivo microenvironment. To test this hypothesis we characterized cellular responses to asbestos in a controlled environment. We found significantly greater changes in genome-wide expression in response to asbestos exposure in pleural mesothelial cells as compared to peritoneal mesothelial cells. In particular, a greater response in many common genes (IL-8, ATF3, CXCL2, CXCL3, IL-6, GOS2) was seen in pleural mesothelial cells as compared to peritoneal mesothelial cells. Unique genes expressed in pleural mesothelial cells were mainly pro-inflammatory (G-CSF, IL-1β, IL-1α, GREM1) and have previously been shown to be involved in development of MM. Our results are consistent with the hypothesis that differences in incidences of pleural and peritoneal MM upon exposure to asbestos are the result of differences in mesothelial cell physiology that lead to differences in the inflammatory response, which leads to cancer.

Topics: Adult; Aged; Asbestos, Crocidolite; Cell Line; Cell Survival; Female; Gene Expression Regulation, Neoplastic; Genetic Predisposition to Disease; High-Throughput Nucleotide Sequencing; Humans; Inflammation; Lung Neoplasms; Male; Mesothelioma; Mesothelioma, Malignant; Middle Aged; Peritoneal Neoplasms; Pleural Neoplasms; Sequence Analysis, RNA

Asbestos exposure is related to various diseases including asbestosis and malignant mesothelioma (MM). Among the pathogenic mechanisms proposed by which asbestos can cause diseases involving epithelial and mesothelial cells, the most widely accepted one is the generation of reactive oxygen species and/or depletion of antioxidants like glutathione. It has also been demonstrated that asbestos can induce inflammation, perhaps due to activation of inflammasomes.. The oxidation state of thioredoxin was analyzed by redox Western blot analysis and ROS generation was assessed spectrophotometrically as a read-out of solubilized formazan produced by the reduction of nitrotetrazolium blue (NTB) by superoxide. Quantitative real time PCR was used to assess changes in gene transcription.. Here we demonstrate that crocidolite asbestos fibers oxidize the pool of the antioxidant, Thioredoxin-1 (Trx1), which results in release of Thioredoxin Interacting Protein (TXNIP) and subsequent activation of inflammasomes in human mesothelial cells. Exposure to crocidolite asbestos resulted in the depletion of reduced Trx1 in human peritoneal mesothelial (LP9/hTERT) cells. Pretreatment with the antioxidant dehydroascorbic acid (a reactive oxygen species (ROS) scavenger) reduced the level of crocidolite asbestos-induced Trx1 oxidation as well as the depletion of reduced Trx1. Increasing Trx1 expression levels using a Trx1 over-expression vector, reduced the extent of Trx1 oxidation and generation of ROS by crocidolite asbestos, and increased cell survival. In addition, knockdown of TXNIP expression by siRNA attenuated crocidolite asbestos-induced activation of the inflammasome.. Our novel findings suggest that extensive Trx1 oxidation and TXNIP dissociation may be one of the mechanisms by which crocidolite asbestos activates the inflammasome and helps in development of MM.

Topics: Acetylcysteine; Antioxidants; Apoptosis; Asbestos, Crocidolite; Blotting, Western; Caspase 1; Cell Line, Tumor; Dehydroascorbic Acid; Dinitrochlorobenzene; Enzyme Activation; Epithelium; Gene Knockdown Techniques; Humans; Inflammation; L-Lactate Dehydrogenase; Reactive Oxygen Species; Real-Time Polymerase Chain Reaction; RNA, Small Interfering; Thioredoxin Reductase 1; Thioredoxins

Possible effects of multi-wall carbon nanotubes (MWCNTs) on immune and inflammatory responses were examined in mice. Female ICR mice were given a single intraperitoneal administration (2 mg/kg body weight) of either MWCNTs, carbon black (CB), or crocidolite (blue asbestos) and controls received a vehicle of 2% sodium carboxymethyl cellulose (CMC Na). In the peritoneal cavity of MWCNT-administered mice, the liver had changed to a rounded shape and fibrous adhesions were seen on internal organs. Peritoneal cells overexpressed mRNA for genes of T helper (Th)2 cytokines (interleukin [IL]-4, IL-5, and IL-13), Th17 cytokine (IL-17), pro-inflammatory cytokines/chemokines (IL-1β, IL-33, tumor necrosis factor α, and monocyte chemotactic protein-1), and myeloid differentiation factor 88 for at least 2 weeks after the administration of MWCNTs, while those of Th1 cytokine genes (IL-2 and interferon γ) were overexpressed several weeks later and expression levels remained high up to 20 weeks. In MWCNT-treated mice, the numbers of leukocytes, monocytes, and granulocytes in the peripheral blood and the expression of the leukocyte adhesion molecules, cluster of differentiation (CD)49d and CD54, on granulocytes were increased 1 week after administration and remained high up to week 20. Production of ovalbumin-specific IgM and IgG(1) was enhanced by MWCNTs. These changes were not observed after CB or crocidolite administration. Thus, this study showed that MWCNTs exhibited sustained stimulating effects on immune and inflammatory responses, unlike the other mineral fibers with structural similarities.

Topics: Animals; Asbestos, Crocidolite; Cytokines; Female; Immunoglobulin G; Immunoglobulin M; Inflammation; Leukocyte Count; Liver; Mice; Mice, Inbred ICR; Nanotubes, Carbon; Ovalbumin; RNA, Messenger; Soot

Extracellular superoxide dismutase (EC-SOD) is expressed at high levels in lungs. EC-SOD has a polycationic matrix-binding domain that binds to polyanionic constituents in the matrix. Previous studies indicate that EC-SOD protects the lung in both bleomycin- and asbestos-induced models of pulmonary fibrosis. Although the mechanism of EC-SOD protection is not fully understood, these studies indicate that EC-SOD plays an important role in regulating inflammatory responses to pulmonary injury. Hyaluronan is a polyanionic high molecular mass polysaccharide found in the extracellular matrix that is sensitive to oxidant-mediated fragmentation. Recent studies found that elevated levels of low molecular mass hyaluronan are associated with inflammatory conditions. We hypothesize that EC-SOD may inhibit pulmonary inflammation in part by preventing superoxide-mediated fragmentation of hyaluronan to low molecular mass fragments. We found that EC-SOD directly binds to hyaluronan and significantly inhibits oxidant-induced degradation of this glycosaminoglycan. In vitro human polymorphic neutrophil chemotaxis studies indicate that oxidative fragmentation of hyaluronan results in polymorphic neutrophil chemotaxis and that EC-SOD can completely prevent this response. Intratracheal injection of crocidolite asbestos in mice leads to pulmonary inflammation and injury that is enhanced in EC-SOD knock-out mice. Notably, hyaluronan levels are increased in the bronchoalveolar lavage fluid after asbestos-induced pulmonary injury, and this response is markedly enhanced in EC-SOD knock-out mice. These data indicate that inhibition of oxidative hyaluronan fragmentation probably represents one mechanism by which EC-SOD inhibits inflammation in response to lung injury.

Topics: Animals; Antibiotics, Antineoplastic; Asbestos, Crocidolite; Bleomycin; Bronchoalveolar Lavage; Chemotaxis; Extracellular Matrix; Gene Expression Regulation, Enzymologic; Humans; Hyaluronic Acid; Inflammation; Lung; Lung Injury; Mice; Mice, Knockout; Neutrophils; Oxidation-Reduction; Pneumonia; Pulmonary Fibrosis; Superoxide Dismutase; Superoxides

Asbestosis is a chronic form of interstitial lung disease characterized by inflammation and fibrosis that results from the inhalation of asbestos fibers. Although the pathogenesis of asbestosis is poorly understood, reactive oxygen species may mediate the progression of this disease. The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) can protect the lung against a variety of insults; however, its role in asbestosis is unknown. To determine if EC-SOD plays a direct role in protecting the lung from asbestos-induced injury, intratracheal injections of crocidolite were given to wild-type and ec-sod-null mice. Bronchoalveolar lavage fluid (BALF) from asbestos-treated ec-sod-null mice at 24 h, 14 days, or 28 days posttreatment showed increased inflammation and total BALF protein content compared to that of wild-type mice. In addition, lungs from ec-sod-null mice showed increased hydroxyproline content compared to those of wild-type mice, indicating a greater fibrotic response. Finally, lungs from ec-sod-null mice showed greater oxidative damage, as assessed by nitrotyrosine content compared to those of their wild-type counterparts. These results indicate that depletion of EC-SOD from the lung increases oxidative stress and injury in response to asbestos.

Topics: Animals; Asbestos, Crocidolite; Bronchoalveolar Lavage Fluid; Hydroxyproline; Inflammation; Lung; Lung Diseases; Lung Injury; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Oxidative Stress; Superoxide Dismutase; Tyrosine

An unusual cluster of malignant mesothelioma was evidenced in Biancavilla, a Sicily village where no inhabitant had been significantly and professionally exposed to asbestos. Mineralogical and environmental studies led to the identification of a new prismatic amphibole, named fluoro-edenite. We previously reported, by using the human lung epithelial A549 cells, that prismatic fluoro-edenite was unable to induce changes that could be somehow related to cellular transformation, and this was in accordance with studies carried out in vivo. More recently, a fibrous amphibole with a composition very similar to that of prismatic fluoro-edenite, was identified in Biancavilla. This fibrous fluoro-edenite was shown to induce mesothelioma in rats. In keeping with this effect in vivo, in the present work we observed multinucleation and spreading, common features of transformed cells, as well as pro-inflammatory cytokine release in A549 cells. Such cell changes occurred without interfering with the passage of the resulting multinucleated cells through the cell cycle and without condemning cells to death. Hence, in lung epithelial cells, fibrous fluoro-edenite behaved similarly to the unrelated asbestos type crocidolite, whose connection with severe inflammation and cancer of the lung is renowned.

Topics: Asbestos, Amphibole; Asbestos, Crocidolite; Cell Proliferation; Cell Survival; Cells, Cultured; Cytokines; Epithelial Cells; Humans; Inflammation; Interleukin-6; Interleukin-8; Lung; Mesothelioma

The mesothelial lining is a target for the fibrotic and carcinogenic effects of mineral fibers. Fiber geometry, dimensions, chemical composition, surface reactivity, and biopersistence at the target tissue have been proposed to contribute to these toxic endpoints. We established a dose-response relationship between the number of fibers delivered to the parietal peritoneal lining, inflammation, and mesothelial cell proliferation induced by intraperitoneal injection of crocidolite asbestos fibers in mice. Persistence of these inflammatory and proliferative responses depended on persistence of fibers at the target tissue. Intraperitoneal injection of wollastonite fibers induced an early inflammatory and proliferative response that subsided after 21 days. Approximately 50% of wollastonite fibers were recovered by bleach digestion after 21 days and only 2% were recovered after 6 months. In contrast, the number of fibers recovered from tissue digests had not declined 6 months after injection of crocidolite asbestos. These results support the hypothesis that biopersistent fibers cause persistent inflammation and chronic mesothelial cell proliferation.

Topics: Animals; Antimetabolites; Asbestos, Crocidolite; Bromodeoxyuridine; Calcium Compounds; Carcinogens; Cell Count; Cell Division; Half-Life; Immunohistochemistry; Inflammation; Male; Mice; Mice, Inbred C57BL; Microscopy, Electron, Scanning; Peritoneal Lavage; Respiratory Muscles; Silicates

Asbestos refers to a group of fibrous minerals implicated in the development of several lung diseases, including fibrosis (asbestosis), cancer, and malignant mesothelioma. Although major health risks exist in occupationally exposed individuals, low-level exposures of asbestos may still contribute to health problems. The mechanism by which asbestos causes lung disease is not clearly understood but has been proposed to involve the alveolar macrophage (AM). We propose that asbestos induces apoptosis of AM, resulting in the development of an inflammatory state. In this study, we examined two forms of asbestos, chrysotile (CHR) and crocidolite (CRO), along with a control fiber, wollastonite (WOL), to characterize their relative cytotoxicity and ability to stimulate apoptosis in vitro. AM were cultured for 24 h with these particulates and examined for cell viability (trypan blue exclusion) and apoptosis (morphology, levels of cytosolic oligonucleosomal DNA fragments, and DNA ladder). In the absence of a decrease in cell viability, both CHR and CRO produced changes in cell morphology consistent with apoptosis. In addition, levels of cytoplasmic oligonucleosomal DNA (Cell Death Detection enzyme-linked immunosorbent assay) were significantly enhanced for CHR (3-25 micrograms/ml) and CRO (25-75 micrograms/ml) in a dose-dependent manner (a process that was inhibitable by 10 microM Z-Val-Ala-Asp fluoromethyl ketone, an interleukin-converting enzyme inhibitor). In contrast, WOL (up to 400 micrograms/ml) produced no significant DNA fragmentation in a 24-h culture. Neither CHR nor CRO caused DNA ladder formation in 24-h cell cultures. However, in 48-h cell cultures, both CHR- and CRO-exposed cells, but not WOL, resulted in the formation of DNA ladders characteristic of apoptosis. In summary, these results suggest that, unlike nonfibrogenic particulates, low doses of asbestos fibers cause apoptosis in cultured human AM that may be an early step in the development of lung fibrosis.

Topics: Apoptosis; Asbestos, Crocidolite; Asbestos, Serpentine; Bronchoalveolar Lavage Fluid; Calcium Compounds; Cell Survival; DNA; Humans; Inflammation; Macrophages, Alveolar; Reference Values; Silicates

The mesothelium is a target of the toxic and carcinogenic effects of asbestos fibers. Fibers greater than 8 mu in length and less than 0.25 mu in diameter have been found to be highly tumorigenic in rodents, while shorter asbestos fibers or spherical mineral particles have not been shown to produce mesotheliomas. For investigation of early mesothelial reactions associated with the development of mesotheliomas, C57BL/6 mice were given intraperitoneal injections of 200 micrograms of short or long crocidolite asbestos fibers, toxic silica particles, or nontoxic titanium dioxide particles. At intervals between 3 hours and 21 days after a single injection, the mesothelial surface of the diaphragm was examined by stereomicroscopy, scanning electron microscopy, and autoradiography. Within 6 hours after injection of asbestos fibers, mesothelial cells in the lacunar regions of the diaphragm retracted opening stomata 10.7 +/- 2.3 mu in diameter leading to the submesothelial lymphatic plexus. Short asbestos fibers (90.6% less than or equal to 2 mu in length), silica, or titanium dioxide particles (less than or equal to 5 mu in diameter) were cleared through these stomata without provoking an inflammatory reaction or mesothelial injury. In contrast, long asbestos fibers (60.3% greater than or equal to 2 mu in length) were trapped at the lymphatic stomata in the lacunar regions on the peritoneal surface of the diaphragm. At these sites, an intense inflammatory reaction developed with accumulation of activated macrophages and a 5.5-fold increase in albumin recovered in the peritoneal lavage fluid after 3 days. As early as 12 hours after injection of long asbestos fibers, the adjacent mesothelial cells were unable to exclude trypan blue and lost their surface microvilli, developed blebs, and detached. Recovery of lactate dehydrogenase activity in the peritoneal lavage fluid was increased 5.8-fold after 3 days and returned to normal levels after 14 days. Regenerating mesothelial cells appeared at the periphery of asbestos fiber clusters 3 days after injection. Maximal incorporation of 3H-thymidine by mesothelial cells occurred after 7 days, followed by partial restoration of the mesothelial lining after 14-21 days. As late as 6 months after a single injection of crocidolite asbestos fibers, clusters of fibers remained in the lacunar regions, partially covered by mesothelium but surrounded by macrophages and regenerating mesothelial cells. The anatomic distribution and si

Topics: Animals; Asbestos; Asbestos, Crocidolite; Diaphragm; Epithelium; Inflammation; Lymphatic System; Male; Mesothelioma; Mice; Mice, Inbred C57BL; Microscopy, Electron, Scanning; Microvilli; Peritoneal Cavity; Silicon Dioxide